Recent developments in the real time analysis of the cardiac signal under the influence of autonomic control, have led to the development of a new painful stress index. A monitor has recently been developed by Mdoloris® company and provides an Analgesia and Nociception Index (ANI index in children and adults and NIPE index - for Newborn Infant Parasympathetic Evaluation - in newborns). It is based on the study of the heart rate variability and the variations of the sympathetic and parasympathetic indices to stimuli. Clinical correlations have been completed for adult patients during or after general anesthesia. The validation of this nociception index has not been validated in a neonatal unit where special attention is paid to pain control.